Your email address is used at several places in the customer portal/webshop. By design, these are not linked to each other, and need to be changed separately. Your username, which is your initial email address, however cannot be changed.
Username (email address)
Used to log in. Cannot be changed.
This is the generic email address connected to your account. It is used e.g. for sending password reset emails. Change under My Account:
Note: Do not enter or change the password when changing the account email. If you do, the email will not be changed.
This is used e.g. for sending the invoice after each order. Change on the checkout page when making your next order or under My Account, Settings tab:
Cannot be changed. If required, you need to unsubscribe from the old email address and then subscribe from the new address.